I'm not sure of what detail you want. You absolutely need to remove the printing and any trim lines and all on the loco before repainted - their texture will show through.
Anyway, I redo tenders all the time, but in most cases the colors I repaint are black: you can check the recent posts where I bashed two Lionchief locos: I repainted both tenders. I use rattle cans. I sand down the lettering and any painted trim lines on the tender and prime it with Rustoleum gray auto primer, and let that harden a whole day even though the can says you can paint on top of it in one hour. I use Rustoluem paints then on top, usually satin. Most times, I am also redoing the loco and do both with the same paint at the same time. Doing only a tender and trying to match an original (still unpainted) loco is difficult: you have to try different paints on something until you find a match to color and patina.
The tender (and loco) below is a rather rare exception to the "black" I mostly do. This is a Legacy N&W J repainted in UP greyhound. What black you see is the original Lionel paint, just masked well before starting. I used primer - again a full day to dry - on all but the masked black, then satin grey over everything, even where the armor yellow is now. I let that dry/harden three days. I then masked all of what is grey now and paint the yellow next. Before paint, I put 1/4 inch high vinyl plastic letters on the tender spelling UNION PACIFIC and the numbers on the loco, then sprayed the armor yellow. While that paint was still moist I carefully removed the masking tape and the vinyl letters. No clearcoat over it, just let it harden a week before handling.